In a flat display device, amorphous silicon is generally used to serve as a semi-conductive layer. However, with the development of flat display device towards high resolution, high integration, and low power consumption, these properties can hardly be realized by amorphous silicon. Therefore, polysilicon is used to meet the development requirement of flat display device, and thus Low Temperature Poly-Silicon (LTPS) has been widely used.
In LTPS technology, amorphous silicon is melted through Excimer Laser Annealing (ELA) method, and polysilicon can be formed after crystallization. According to the traditional technology, before ELA is performed, the original silicon dioxide layer on a surface of silicon semi-conductive layer is etched by hydrofluoric acid. Then, the silicon is oxidized by ozone (O3), so that a silicon dioxide layer with a needed feature can be formed on the surface of the silicon semi-conductive layer. During ELA procedure, the silicon dioxide layer generated therein can play a role of heat preservation. However, since the oxidation capacity of ozone is limited, a thickness of the silicon dioxide layer generated therein is only about 3 nm in general. Since the thickness of the silicon dioxide layer is too small, the formation of protrusions by melted amorphous silicon at grain boundary during crystallization procedure cannot be prevented. As a result, the semi-conductive layer manufactured therein has a relatively high roughness, and the display quality of the flat display device would be adversely affected.